Load-carrying trailers designed to be towed behind vehicles are well known. While trailers were used extensively long before motor vehicles were popularized in the twentieth century, use of trailers has increased dramatically in the past hundred years. Naturally, this dramatic increase in trailer use has resulted in development of a large array of trailer designs of varying configurations, many of which are specially adapted to perform a specific function or to be utilized in conjunction with a specific activity.
A very common trailer design incorporates a substantially flat bed or deck on which a load to be carried is placed. Such trailers are typically equipped with a frame, one or more axles affixed to said frame, a tongue or other device for connecting the trailer to a towing vehicle, and a bed or deck on which a load may be positioned and secured.
To ensure that the load-carrying portions of the trailer do not contact the surface on which the trailer is being operated, the wheels and axles of the trailer are generally designed to position the frame and the load-carrying deck some distance above the surface on which the trailer is operated. The result is that the load-carrying surface of the trailer is elevated in relation to the ground. Thus, when the trailer is to be loaded or unloaded, the intended load must be lifted from ground level to the level on which the trailer deck or bed is disposed or vice versa. For lightweight objects, this is not a significant problem, since those objects can simply be manually moved from ground level to trailer deck level. For heavier objects, however, such as vehicles, including motorcycles, manual lifting of the intended load is not practical.
In response to this problem, a number of methods have been developed for facilitating the loading of cargo onto the deck or bed of a trailer. In one scheme, the trailer bed and/or frame are pivotally mounted in relation to the trailer axle, allowing the rearmost edge of the trailer deck to be rotated down into contact with the ground. This allows the cargo to be rolled or slid from the ground surface to the deck of the trailer. Once the load has been so transferred, the bed and/or frame can be pivoted to a more or less horizontal position. While this system is simple, it relies upon pivoting the deck of the trailer with respect to the axle of the trailer. Because the distance between the axle of the trailer and the rearmost edge of the trailer is typically quite short, the deck of the trailer is disposed at a steep incline when the rearmost edge of the trailer is in contract with the ground. Thus, due to the angle of the trailer deck it is often awkward or difficult to transfer the load up the incline created by pivoting the trailer deck with respect to the axle of the trailer.
Another technique which is commonly used is the addition of removable or extensible ramp elements which may be affixed to the back edge of the trailer deck. Such ramps or extensions may be completely removable or may be hinged to the rear edge of the trailer and pivoted into the loading and transport positions as needed. While this methodology is simple, it is subject to the same limitations of the tilting frame/bed trailer arrangement above-described in that the ramp elements often present an incline over which it may be difficult to maneuver cargo to be loaded onto the trailer.
One known trailer with a height-adjusting mechanism for changing the height of a load supporting portion of a trailer includes a single axle that is rotatable connected to a trailer frame of the trailer for rotation between a towing position and a loading position. The axle has a first portion and a pair of axle shafts that are resiliently mounted with respect to the first portion for rotation over a limited angular range of motion and are biased toward a neutral position. A pair of opposed pivot arms are rotatable in response to rotation of the axle between the towing position and the loading position. The pivot arms are rotatable with the axle shaft of the axle in response to rotation of the axle shaft with respect to the central portion of the axle.